Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$83.78	5.410%	$88.3125	$88.31	$88.30	$88.30
Purchase #2	$153.80	10.428%	$169.8383	$169.84	$169.85	$169.80
Purchase #3	$168.40	9.631%	$184.6186	$184.62	$184.60	$184.60
Purchase #4	$43.72	10.737%	$48.4142	$48.41	$48.40	$48.40
Purchase #5	$11.64	3.749%	$12.0764	$12.08	$12.10	$12.10
Purchase #6	$51.51	10.382%	$56.8578	$56.86	$56.85	$56.90
Purchase #7	$101.35	7.834%	$109.2898	$109.29	$109.30	$109.30
7 purchase totals =	$614.20		$669.4076	$669.41	$669.40	$669.40